Among the proposed alternative fuels for shipping, identified LNG, LPG, methanol, biofuel and hydrogen as the most promising solutions. Among new technologies, the classification society believes battery systems, fuel cells and wind-assisted propulsion to offer potential for ship applications.

Fuel cell systems for ships are under development but will take time to reach a level of maturity sufficient for substituting main engines. Battery systems are finding their way into shipping; however, on most seagoing ships their role is limited to enhancing efficiency and flexibility. Wind-assisted propulsion, while not a new technology, will require some development work to make a meaningful difference for modern vessels.

When it comes to CO2 emissions, LNG is the fossil fuel producing the lowest amounts. However, the release of unburned methane (so called methane slip) could reduce the benefit over HFO and MGO in certain engine types. Methane (CH4) has 25 to 30 times the greenhouse gas effect of CO2. Nevertheless, engine manufacturers claim that the tank-to-propeller (TTP) CO2-equivalent emissions of Otto-cycle dual-fuel (DF) and pure gas engines are lower than those of oil-fuelled engines.

If produced from renewable energy or biomass the carbon footprints of methanol and hydrogen can be significantly lower than those of HFO and MGO.

The cleanest fuel is hydrogen produced using renewable energy. Liquefied hydrogen could be used in future shipping applications. However, because of its very low energy density it requires large storage volumes, which may prevent hydrogen from being used directly in international deep-sea shipping. In a sustainable energy world where the entire energy demand is covered by renewable, CO2-free sources, hydrogen and CO2 will be the basic ingredients for fuel production, most likely in the form of methane or diesel-like fuels produced in a Sabatier/Fischer-Tropsch process. The Sabatier process is a reaction between hydrogen and carbon dioxide at elevated temperatures – optimally 300 to 400°C – and pressures in the presence of a nickel catalyst to produce methane and water. An alternative, the Fischer-Tropsch process converts a mixture of carbon monoxide and hydrogen into liquid hydrocarbons in a series of chemical reactions.

Looking ahead, LNG has already overcome the hurdles of international legislation, and methanol and biofuels will follow suit very soon. It will be a while before LPG and hydrogen are covered by appropriate new regulations within the IMO IGF Code as well. The existing and upcoming environmental restrictions can be met by all alternative fuels using existing technology. However, the IMO target of reducing GHG emissions by 50 per cent by 2050 is ambitious and will likely require widespread uptake of zero-carbon fuels and further energy efficiency enhancements. Fuel cells can use all available alternative fuels and achieve efficiencies comparable to, or better than, those of current propulsion systems.

However, fuel cell technology for ships is still in its infancy. Promising and advanced projects are, e.g., those running under the umbrella of the e4ships lighthouse project in Germany, with Meyer Werft and ThyssenKrupp Marine Systems heading the projects for seagoing ships.

For thousands of years, wind was the primary energy source used to propel ships, apart from manpower. Today, wind-assisted propulsion is understood to be a potential method of reducing the fossil-fuel-based energy consumption of ships. Wind is an inexhaustible source of energy.

Wind-assisted propulsion could potentially reduce fuel consumption, especially when used for slow ships, but the business case remains difficult. Batteries as a means of storing energy can be considered as an alternative fuel source in the widest sense. Especially on ships operating on short, regular voyages, they have major potential as a means to boost the efficiency of the propulsion system. In deep-sea shipping, batteries alone are not an adequate substitute for combustible energy sources. Finally, with low-sulphur and alternative fuels becoming more widely available, the well-known combined-cycle gas and steam turbine technology.

A wide range of alternative fuels for ships are currently under discussion. The main aspects to compare a fuel to the existing benchmark of crude-oil-based ship fuels are the environmental impact, the fuel price, the available/needed infrastructure and availability, the regulatory framework, the required technology, the CAPEX and the part of the OPEX related to the use of the fuel, for instance exhaust gas cleaning.

The fuels presented here are in our view the most promising alternatives to conventional ship fuel.

Liquefied natural gas (LNG) has more or less the same composition as natural gas used for households and power generation and in the industry. Its main component is methane (CH4), the hydrocarbon fuel with the lowest carbon content. It should be noted that it is possible to produce methane from hydrogen (H2) and carbon dioxide (CO2) (see comparison below under “Hydrogen and PtF”). If liquefied, the physical properties are nearly equivalent to those of LNG. LNG is a cryogenic liquid with a boiling temperature of approximately –160°C at atmospheric pressure.

Synthetic natural gas (SNG), also known as substitute natural gas (both usually shortened to SNG), describes a variety of natural gas alternatives that are as close as possible in composition and properties to natural gas. SNG can be derived from coal, (waste) biomass or synthesized using surplus renewable energy. The results of the latter two methods are often referred to as bio-SNG/biogas and e-gas/syngas. Depending on the source fuel, SNG can be a low-carbon or even carbon-free substitute for fossil fuels. Thanks to its composition, it can be mixed and used interchangeably with natural gas in all applications. Liquefied or compressed SNG can be transported or stored in the gas grid.

Liquefied petroleum gas (LPG) is by definition any mixture of propane and butane in liquid form. For instance, in the USA, the term LPG is generally associated with propane. Mixing butane and propane enables specific saturation pressure and temperature characteristics. LPG can be handled in pressure tanks at ambient temperature. As an example, the saturation pressure of propane at 45°C is approximately 16 bar g. This is the most recommended for the LPG tanker ships.

With its chemical structure CH3OH, methanol is the simplest alcohol with the lowest carbon content and highest hydrogen content of any liquid fuel. Methanol is a basic building block for hundreds of essential chemical commodities and is also used as a fuel for transport. It can be produced from a number of different feedstock resources like natural gas or coal, or from renewable resources such as biomass or CO2 and hydrogen. These fuels are introduced into the Methanol tankers and similar medium range clean product tankers.

Biofuels are derived from primary biomass or biomass residues that are converted into liquid or gaseous fuels. A large variety of processes exist for the production of conventional (first-generation) and advanced (second and third-generation) biofuels, involving a variety of feedstocks and conversions. The most promising biofuels for ships are biodiesel (e.g. HVO – hydrotreated vegetable oil, BTL – biomass-to-liquids, FAME – fatty acid methyl ester) and LBG (liquid biogas, which primarily consists of methane). Biodiesel is most suitable for replacing MDO/MGO, LBG for replacing fossil LNG, and SVO (straight vegetable oil) for replacing HFO.

Hydrogen (H2) can be produced in several different ways. Today, nearly all hydrogen is produced by reforming natural gas. The production of hydrogen through water electrolysis could be combined with the growing renewable energy sector, which delivers, by nature, intermittent electrical power only. Conversion to hydrogen could facilitate storage and transport of this renewable energy. Hydrogen from electrolysis and renewable energy (wind, solar, water) is the basic building block for a range of fuels. Hydrogen can be used directly as compressed or liquefied gas. In combination with carbon dioxide, it can be converted to methane gas (i.e. power-to-gas [PtG]). Methane can be liquefied and used in the same way as LNG. Hydrogen and carbon dioxide also can be converted to liquid “diesel-like” fuels (i.e. power-to-liquid [PtL]). The PtG and PtL processes can be summarized as power-to-fuel (PtF).

Batteries provide the ability to directly store electrical energy for propulsion, opening up many other opportunities to optimize the power system. Recent advancements in battery technology and falling costs thanks to the growing worldwide demand for batteries make this technology attractive to the shipping industry. The excess energy generated from the shaft generator is used to charge the batteries and then used as load required.

Fuel cells convert the chemical energy contained in a fuel directly into electrical and thermal energy through electrochemical oxidation. This direct conversion process enables electrical efficiencies of up to 60%, depending on the type of fuel cell and fuel used. It also minimizes vibration and noise emissions, a major setback of combustion engines.

Steel Ships PMC is always ready for IMO 2030, 2050 and develop the Zero Carbon Emission technologies while ensuring cos effective ship owning experience.